Vertical/Short Take-Off and Landing (V/STOL) Vehicles are fixed-wing aircraft that can lift off from the ground and land in a vertical hover, and transition from the vertical hover mode to a horizontal flight mode and back to vertical hover mode. Configurations have included vectored-thrust aircraft like the British AV8B Harrier now built by Boeing, and the F-35B Joint Strike Fighter from Lockheed-Martin. These concepts direct the thrust from a jet engine downward to hover and rearward for horizontal flight. Tilt-wing/tilt-rotor aircraft like the V-22 Osprey, jointly from Bell Helicopter and Boeing, direct thrust from two rotatable proprotor assemblies situated in engine nacelles at the ends of the main wing.
Roadable Airborne Vehicles are aircraft that can transform themselves such that they can be driven on roads intended for automobiles. Terrafugia of Terrafugia, Inc. is one such vehicle.
Vertical/Short Take-off and Landing Roadable Airborne Vehicles are aircraft that not only can transform themselves from an airplane to an automobile, but can also take off and land vertically. The Skycar by Moller International is an attempts to accomplish this combination of different operational modes.
From the foregoing it will be apparent that rather than decentralizing a multitude of power plants, safety and efficiency can be realized by concentrating a few power plants in the near vicinity of the vehicle center of gravity. Further, it will be apparent that benefits will be gained by utilizing inline counter-rotating propellers. It will also be apparent that by assigning multiple functions for most of the vehicle components, the most weight efficient structure can be achieved.